When it is desired to turn about its horizontal axis a boilermaking part of large dimensions, and therefore of great weight, it is necessary to raise the part with the aid of a crane, to turn the part slightly, and to replace it on its horizontal support. The handling of a part of this kind is obviously a very lengthy operation and may in addition not be carried out perfectly, because the angle of rotation by which the part is turned about its axis may not be very accurate and there is a danger that the part may not be replaced accurately on its support after each handling operation.